The short answer: test the endpoint yourself, read the limit in numbers, check CORS and HTTPS, confirm the docs are alive, prefer honest auth, and have an exit plan. Seven checks, ten minutes — here is each one with a real example from our verification data.
In the latest run: 257 entries were dropped because even their homepages were gone (check 5 would have caught them — eventually). Four of our own curated favorites were down (check 1). One major exchange answered 451 from our network — a reminder that "down" can also mean "down for you", which for your users is the same thing.
Open the API's page here → run its playground → read its limit → skim its docs' changelog → check its badge on our status board. If it passes you, it will probably survive your project. If it fails two checks, pick the runner-up from its category — there is always a runner-up.
What is the single most important check?
That the endpoint answers right now, with real data. Everything else is refinement; a dead endpoint is a dead project.
Is a free-key API worse than a keyless one?
Often the opposite: keys make limits per-user instead of shared, so serious providers (NASA, TMDB, GitHub) are frequently more reliable than anonymous free-for-alls.
How do I know a free tier will not vanish?
You cannot know — you can only prepare. Providers with paid tiers subsidize free ones sustainably; one-person passion projects are the fragile ones. Hence check 7: the exit plan.
Browse the live-verified catalog, check the status board, or steal a starter bundle.